Aerospace housing and shaft assembly

ABSTRACT

A seal assembly having a first seal ring of a generally annular shape and defining radial and circumferential directions, and a second seal ring positioned in facing relation to the first seal ring. One of the first seal ring and the second seal ring includes a plurality of hydropads. Each hydropad has an inner edge oriented substantially circumferentially, an outer edge oriented substantially circumferentially and spaced radially outward from the inner edge, a leading edge interconnecting the inner edge with the outer edge, and a trailing edge interconnecting the inner edge with the outer edge. Both the leading edge and the trailing edge are substantially straight and are positioned at the same angle relative to a radial axis passing through a mid-point of each edge, respectively.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.08/878,433 filed on Jun. 18, 1997, and issued as U.S. Pat. No. 5,941,532on Aug. 24, 1999, which claims the benefit of U.S. Provisional PatentApplication No. 60/020,153 filed on Jun. 20, 1996.

FIELD OF THE INVENTION

The present invention generally relates to the field of aerospacehousing and shaft assemblies, and more specifically to seals forproviding a barrier between a housing and a shaft in an aerospaceapplication.

BACKGROUND OF THE INVENTION

Mechanical face seals are commonly used to provide a seal between astationary housing and a rotating shaft. Such seals include a rotatingring mounted on the shaft and a stationary ring mounted on the housing.Either the stator or the rotor is biased toward the other to provide abiased seal therebetween.

A typical seal design for inhibiting process fluid, whether liquid orgas, from escaping from a housing along a rotating shaft includes twoseals in fluid communication with an intermediate chamber containing abuffer fluid. One seal pumps the buffer fluid having a certain pressureacross the seal between a stator and rotator into the housing containingthe process fluid. The process fluid in the housing has a lower pressurethan the buffer fluid in the intermediate chamber. The other seal pumpsthe buffer fluid to an environment external to the housing, such asambient, which is at a pressure lower than the buffer fluid in theintermediate chamber.

To accomplish this pumping, each seal includes spiral grooves on eitherthe face of the stator or rotor. The grooves are angled relative to theradius and circumference of the rotating shaft, and when the rotator isrotating, the grooves pump the buffer fluid across the seal. Thispumping of the high-pressure buffer fluid toward the lower-pressureexternal environment or process fluid inhibits the loss of the processfluid from the housing. U.S. Pat. No. 5,375,853 discloses a seal designof this type.

In another design, grooved face seals are used in pumps to provide aseal between a high-pressure gas (e.g., a combustible gas) and theambient atmosphere. In this situation, two seals are commonly used. Agrooved inner seal pumps the high pressure gas to an intermediatechamber, and a grooved outer seal pumps from the intermediate chamber tothe atmosphere. The intermediate chamber routes the high-pressure gas toa flare stack where the pumped gas is burned. The amount ofhigh-pressure gas that is lost through the outer seal is therebyminimized. An example of this type of seal is disclosed in U.S. Pat. No.5,217,233.

SUMMARY OF THE INVENTION

The present invention recognizes that grooved face seals are useful inapplications other than in a fluid pump. For example, it has beendiscovered that grooved face seals provide significant benefits in termsof reduced heat generation and longer seal life when used in aerospaceapplications, such as on gear boxes, starters, constant speed drives andintegrated drive generators. In fact, in some situations, significantbenefits can be achieved by using grooved face seals to replace existingnon-grooved seals. Surprisingly, this also has been found to work insituations where the seal is exposed to atmospheric pressuressubstantially less than 14.7 psia, such as when the seal is being usedin an aerospace application (e.g., an aircraft) at altitude. Inaddition, the present invention has discovered a cost-effective methodfor forming the grooves on the seal rings, thereby making the groovedseals applicable to a larger number of applications where cost may be anissue. Furthermore, a unique and simple hydropad configuration has beendeveloped.

In one aspect, the present invention provides an aerospace housing andshaft assembly comprising a housing, a shaft rotatably mounted withinthe housing, a seal assembly operatively positioned between the housingand the shaft, and low pressure air (e.g., atmospheric air) having apressure substantially less than 14 psia and being positioned on oneside of the seal assembly. The seal assembly includes a first seal ringmounted on the housing, and a second seal ring mounted on the shaft infacing relation to the first seal ring. One of the first seal ring andthe second seal ring includes a hydropad. Preferably, the hydropad ispositioned to pump from the inner diameter toward the outer diameter.For example, the low-pressure air can be positioned on the innerdiameter of the seal assembly, in which case the hydropad would pump thelow-pressure air. In a preferred embodiment, the low-pressure air has apressure less than about 10 psia, and more preferably less than about 5psia.

The present invention also provides a method of producing a sealassembly having a seal ring. The method comprises the steps ofpositioning the seal ring in alignment with a media blaster, placing atemplate between the seal ring and the media blaster, and forcing mediafrom the media blaster, through the openings in the template, and intocontact with the seal ring. The seal ring can then be mounted in a sealassembly. In one embodiment, ceramic beads are used as the blast media.The positioning step can include the step of mounting the seal ring on aholder. Preferably the holder is rotated while the media is being forcedat the seal ring. To obtain better results, a timer can be used toinsure that the blast time is consistent.

The present invention also recognizes that hydropads do not need to bespiral in shape. More specifically, the hydropads can include an inneredge oriented substantially circumferentially, an outer edge orientedsubstantially circumferentially and spaced radially outward from theinner edge, a leading edge interconnecting the inner edge with the outeredge, and a trailing edge interconnecting the inner edge with the outeredge. Both the leading edge and the trailing edge are substantiallystraight and oblique to a radial direction. Preferably, to simplify thedesign, the inner edge and the outer edge are also both substantiallystraight. In one embodiment, the leading edge is positioned at an anglerelative to the radial direction passing through a mid-point of theleading edge, and the trailing edge is positioned at the same anglerelative to the radial direction passing through a mid-point of thetrailing edge.

A more detailed description of a specific embodiment of the presentinvention is illustrated and described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the use of hydropad seals in various applications ina gas turbine engine.

FIG. 2 is a partial cross-section of a rotating shaft positioned in astationary housing.

FIG. 3 illustrates a front view of a mating ring having hydropads.

FIG. 4 is an enlarged view of a hydropad.

FIG. 5 is a front view of a template used to form the hydropads on amating ring.

FIG. 6 illustrates a partial cross section of a mating ring holder andblasting assembly.

FIG. 7 is an enlarged section of the mating ring holder.

DETAILED DESCRIPTION

FIG. 1 illustrates the use of hydropad seals in an aerospace gas turbineengine 10. It has been discovered that hydropad seals can be used in avariety of positions within the engine 10, and can be used to replacestandard (non-hydropad) seals. In FIG. 1, the engine 10 employs use ofthe hydropad seals as compressor inlet seals 11, compressor/drive seals12, interstage seals 14, turbine seals 16, and gearbox seals 18. Usesalso include accessory seals such as constant speed drives, alternators,starters, generators, de-oilers, fuel pumps, hydraulic pumps, gearboxes,main shafts and fuel control seals (not shown). Hydropad seals providevirtually leakage free operations at temperatures ranging up to about600 degrees Fahrenheit. The hydropad seals operate with a shaft speed upto 120,000 rpm for small sizes, and can be designed to handle reversepressures. The hydropad seals can also operate in virtually any fluid,liquid or gas.

FIG. 2 illustrates a cross-section of a rotating shaft 20 positionedwithin a stationary housing 22, and a seal assembly 24 mountedtherebetween. The seal assembly 24 includes two seal rings: a matingring 28 mounted on the shaft 20 and a seal nose 30 mounted on thehousing 22. A hydropad 26 is formed on the mating ring 28. The matingring 28 is typically a ductile material, such as hardened steel, butinstead can be composed of tungsten carbide or silicon carbide, or canbe steel with a ceramic coating.

FIG. 3 illustrates a front view of the mating ring 28 having a pluralityof hydropads 26. The dashed lines represent an inner circumference 34and an outer circumference 36 which define the position of the seal nose30 relative to the hydropads 26, generally called a sealing interfacearea 38. As illustrated in FIG. 3, the hydropads 26 overlap the innercircumference 34 of the sealing interface area 38 on the mating ring 28.A sealing dam region 40 defines the region from the outer circumference36 of the sealing interface area 38 to the outer edge of the hydropad26.

In FIG. 2, a metal bellows 32 is positioned between the housing 22 and aseal nose 30, and allows for axial movement of the seal nose 30. Whenthe shaft 20 is not rotating, the mating ring 28 contacts the seal nose30 at the sealing interface area 38. A working fluid 42 (e.g., oil) ispresent outside (i.e., on the outer diameter of) the mating ring 28. Air44 is positioned on the inner diameter of the seal. The air can befiltered by a filter 45 as schematically shown. The air 44 is preferablyat atmospheric pressure, which is substantially less than 14.7 psia(standard absolute pressure at sea level) in the case of an aircraftflying at altitude. As used herein, the phrase “substantially less than14.7 psia” means that the atmospheric air is what would be experiencedby an aircraft flying at altitude. The seal of the present invention hasbeen successfully tested to pressures of about 2 psia.

When the shaft 20 is rotating, the hydropads 26 force the air 44 betweenthe mating ring 28 and the seal nose 30 to thereby cause a small gap todevelop between the sealing interface area 38 and the seal nose 30. Asthe air 44 is pressurized, a barrier is created inhibiting working fluid42 from passing through the sealing interface area 38. When the shaft 20is not rotating, the sealing dam region 40 seals the working fluid 42 onthe outside of outer circumference 36 of the sealing interface area 38.Because the hydropads 26 do not extend across the entire top surface ofmating ring 28, the separation of the lubricating fluid region 38 fromthe air region 44 is accomplished.

Although the present embodiment illustrates a mating ring 28 rotatingwithin the stationary housing 22, it is also possible for the stationaryhousing 22 to rotate with the mating ring 28 in a fixed position.

FIG. 4 is an enlarged view of a hydropad 26. The configuration of thehydropad 26 is such that a leading edge 44 and a trailing edge 46diverge radially outwardly and are positioned at a constant anglerelative to their respective radial axes. An inner edge 48 and an outeredge 50 are substantially straight and connect edges 44 and 46. In analternate hydropad configuration, the inner edge 48 and outer edge 50can be curved with a center of rotation positioned toward the center ofthe mating ring.

The required depth of the hydropad 26 varies depending upon theapplication. The illustrated hydropads 26 consist of many shallowgrooves at a given depth of approximately 0.0001 inches to 0.0025inches, and at a fixed angle about the inner diameter of the sealingface. The depth, number of grooves and angle of the paths are fixed atfixed values and are chosen to meet the given operating conditions asnecessary.

A method of forming a hydropad on a mating ring is also described, andis most clearly illustrated by FIGS. 5-7. The method utilizes a mediablasting technique to form the hydropads 26 on the mating ring 28. FIG.5 is a front view of the template 56 that is positioned over the frontface of the mating ring 28 during the blasting procedure. Hydropadopenings 62 are positioned in the size and orientation necessary to formthe desired hydropads 26.

FIGS. 6 and 7 illustrate a mating ring holder 64 with a mating ring 28positioned thereon. It is desirable to minimize the radial clearancebetween the mating ring 28 and the holder 64. To facilitate this,o-rings 66 may be used to help center the mating ring 28 onto the holder64. The template 56 is positioned over the face of the mating ring 28,and a clamping plate 68 and fastener 70 are used to secure the template56 and mating ring 28 to the holder 64. The hydropad openings 62 on thetemplate 56 are utilized to define the areas for the formation of thehydropads 26.

The mating ring holder 64 is positioned adjacent to a nozzle 74 of amedia blaster 72 that is aligned toward the openings 62 in template 56.The mating ring holder 64 positions the mating ring 28 and the template56 a fixed and known distance from the nozzle 74. The vertical andhorizontal positioning of the gun assembly 72 is preset prior to thestarting of blasting. A media stream 80 projecting a bead blast from thenozzle 74 is directed such that the media stream 80 impacts midwaybetween the inner edge 48 and outer edge 50 of the hydropads 26.

The media stream 80 can be composed of a variety of abrasive or peeningmaterials, such as aluminum oxide or glass beads. It has been found thatthe use of ceramic beads is particularly advantageous since a moreuniform result is achieved. It is believed that the use of ceramic beadsresults in a high amount of peening, as opposed to material removal.Peening reduces the amount of removed material being recirculated andblasted, and thus is believed to improve the consistency of the blastingoperation. In addition, it is believed that peening results in fewersharp peaks on the blasted part. Alternatively, the media can comprise awater slurry or air slurry or any other suitable material that can beblasted at the seal ring to cause formation of the hydropads, whether bymaterial removal or material compression.

The axial positioning of the nozzle 74 is preset prior to the startingof the blasting operation. The bead blast pressure of the media stream80 is also preset prior to starting of the blasting operation. Also, themating ring 28 begins rotation before the bead blasting operation isstarted. The media blaster 72 is turned on simultaneously with a timer(not shown) which is used to indicate when the media blaster 72 is to beturned off. This method provides the greatest number of uniform matingring hydropad depths.

The media blaster 72 can be rotated to direct the media stream 80 at anend of the template cutout holes 62 that form the hydropads 26. Morespecifically, once the vertical, horizontal and axial locations arefixed, the nozzle 74 can be rotated such that the media stream 80 isdirected at the outer edge of the openings 62. The nozzle 74 can then berotated to direct the media stream 80 at the inner edge of the openings62. It is contemplated that the gun assembly 72 can be set to rotate inmany directions, as necessary for the particular application.

When the bead blasting operation is complete, the template 56 isunclamped from clamping plate 68, and the mating ring 28 is removed. Theclamping or staging surface of the fixture is then cleaned of bead media80 prior to the installation of the next mating ring 28.

In order to obtain the correct depth of the hydropad 26, a polishing orlapping operation after bead blasting may be required. These operationstruncate rough peaks of the bead blasted surface in the hydropad 26 andmay dub edges of the hydropads. The actual depth of the hydropad 26 isbetter controlled by either changing the blasting time, the pressure orthe distance of the gun assembly 72 from the mating ring 28.

In determining the proper bead blasting settings prior to bead blasting,a set-up piece is used. Periodic monitoring of hydropad depths isrecommended to ensure consistency.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. Furthermore, thedescription is not intended to limit the invention to the form disclosedherein. Consequently, variations and modifications commensurate with theabove teachings, and the skill or knowledge of the relevant art, arewithin the scope of the present invention. The embodiments describedherein are further intended to explain best modes known for practicingthe invention and to enable others skilled in the art to utilize theinvention in such, or other, embodiments and with various modificationsrequired by the particular applications or uses of the presentinvention. It is intended that the appended claims be construed toinclude alternative embodiments to the extent permitted by the priorart.

What is claimed is:
 1. A seal assembly comprising: a first seal ring ofa generally annular shape and defining radial and circumferentialdirections; and a rotatably mounted second seal ring positioned infacing relation to said first seal ring to define an interfacetherebetween, wherein one of said first seal ring and second seal ringincludes a plurality of hydropads, said hydropads each including: aninner edge oriented substantially circumferentially; an outer edgeoriented substantially circumferentially and spaced radially outwardfrom said inner edge; a leading edge interconnecting said inner edgewith said outer edge, said leading edge being substantially straight andpositioned at an angle relative to a radial axis passing through amid-point of said leading edge; and a trailing edge interconnecting saidinner edge with said outer edge, said trailing edge being substantiallystraight and positioned at the same angle relative to a radial axispassing through a mid-point of said trailing edge, wherein said one ofsaid first seal ring and second seal ring is positioned to overlap anedge of said interface such that said hydropads are exposed to air in afirst region having a first pressure, and rotation of said second sealring with respect to said first seal ring pumps air into said interfacefrom said first region toward a second region having a second pressureno less than said first pressure thereby substantially preventingpenetration of fluid disposed in said second region through saidinterface.
 2. A seal assembly as claimed in claim 1, wherein said inneredge and said outer edge are both substantially straight.
 3. A sealassembly as claimed in claim 1, wherein said hydropads are positioned topump air from an inner diameter of said seal assembly toward an outerdiameter of said seal assembly.
 4. A seal assembly as claimed in claim1, wherein said second seal ring comprises a ductile metallic material.5. A seal assembly as claimed in claim 4, wherein said first seal ringcomprises a carbon material.
 6. A seal assembly as claimed in claim 1,wherein said hydropads include at least one groove having a depthapproximately equal to or less than 0.0025 inches.
 7. A seal assembly asclaimed in claim 1, wherein said hydropads include at least one groovehaving a depth approximately equal to or less than 0.0001.
 8. A sealassembly comprising: a first seal ring of a generally annular shape anddefining radial and circumferential directions; and a rotatable mountedsecond seal ring positioned in facing relation to said first seal ringto define an interface therebetween, wherein one of said first seal ringand second seal ring includes a plurality of hydropads, wherein aninterface is defined between said first seal ring and said second sealring, said hydropads being positioned to overlap an edge of saidinterface such that said hydropads are exposed to a first fluid in afirst region having a first pressure, and rotation of said second sealring with respect to said first seal ring pumps said first fluid intosaid interface toward a second region having a second pressure no lessthan said first pressure thereby substantially preventing penetration ofa second fluid disposed in said second region through said interface. 9.A seal assembly as claimed in claim 8, in which each hydropad includesan inner edge oriented substantially circumferentially; an outer edgeoriented substantially circumferentially and spaced radially outwardfrom said inner edge; a leading edge interconnecting said inner edgewith said outer edge, said leading edge being substantially straight andpositioned at an angle relative to a radial axis passing through amid-point of said leading edge; and a trailing edge interconnecting saidinner edge with said outer edge, said trailing edge being substantiallystraight and positioned at the same angle relative to a radial axispassing through a mid-point of said trailing edge.
 10. A seal assemblyas claimed in claim 9, wherein said inner edge and said outer edge areboth substantially straight.
 11. A seal assembly as claimed in claim 9,wherein said hydropads are positioned to pump said first fluid from aninner diameter of said seal assembly toward an outer diameter of saidseal assembly.
 12. A seal assembly as claimed in claim 8, wherein saidsecond seal ring comprises a ductile metallic material.
 13. A sealassembly as claimed in claim 12, wherein said first seal ring comprisesa carbon material.
 14. A seal assembly as claimed in claim 8, whereinsaid hydropads include at least one groove having a depth approximatelyequal to or less than 0.0025 inches.
 15. A seal assembly as claimed inclaim 8, wherein said hydropads include at least one groove having adepth approximately equal to or less than 0.0001.
 16. A seal assembly asclaimed in claim 8 in which said first fluid is air.